Katsuya Hirayama

GENERATION OF DOUBLE PEAK DIRECTIONAL WAVE BY DUAL MODE SNAKE-TYPE WAVE MAKER

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

Effects of Transmitted Waves through Breakwaters due to Wave Overtopping for Harbor Tranquility

Transmitted waves through breakwaters due to wave overtopping and their propagation toward quays are sometimes considered in harbor tranquility analysis, because the wave overtopping may occur on breakwaters at harbor entrance in storms. In this study, their effects on cargo handling rate on quays are estimated with considering variations of ratio of wave height due to difference of incident wave height. As a result, it is clear that significant wave transmission cannot occur in case that wave overtopping rate is smaller than 0.02 m/s/m. Hence, the cargo handling rate which is estimated with such way becomes higher because frequent storm waves are attenuated due to wave breaking instead of generating transmitted waves in harbor inside.

An Experimental Study on Evaluation of Wave Overtopping Rate for Seawall on Coral Reef

A wave overtopping rate for a seawall on coral reef may be evaluated with the estimation diagrams of it on sloping beach, which is proposed by Goda & Kishira (1975). To do this, Miyakuni et al. (2008) have suggested that wave set-up and surf-beat should be added to the design water depth which is applied on them. Moreover, Hirayama et al. (2009) have indicated that such design conditions on a coral reef can be calculated by using the Boussinesq-type wave transformation model developed by Hirayama & Hiraishi (2005). In this study, an applicability of such estimation method is verified with the results of model experiments which are carried out on a horizontal basin, and it is confirmed that the calculations of wave transformation on coral reef should be conducted with the topography installed the designed seawalls.

Generation of Random Wave for Several Wave Spectra on Linear Incident Boundary

Generally, wave transformation in shallow water should be estimated for a representative offshore wave spectrum. However it may be difficult for a Boussinesq wave model which requires a relative narrow computational region for calculating wave fields that an incident wave boundary is expanded to offshore. In this paper, multi-directional random waves are generated by using Boussinesq wave model on the linear incident boundary with several wave spectra transformed in shallow water. Wave height distributions behind a spherical shoal can be reproduced with spatial distribution of multi-directional spectra estimated by an energy balance equation. In an actual harbor, the significant wave height in front of a revetment can be estimated larger in generation with several wave spectra.

Model Experiment for Estimation of Uplift Pressure for Piled Jetty of Approach Light on Offshore Airport

On offshore airport, approach light is prepared in the sea and long piled jetty from the revetment of the airport is required for inspection of many lights of it. The uplift pressure by sea wave, however, has not been enough understood yet except by standing wave in front of a piled wharf. In this study, some model experiments are conducted to estimate the uplift pressure under the long thin piled jetty by oblique and random waves.

Evaluation of Harbor Tranquility with Considering Effect of Double-peaked Offshore Spectrum

Generally, a joint distribution of significant wave height, period and direction outside a harbor is analyzed with assumption that a single-peaked spectrum is observed in each time. However, the significant wave periods should be underestimated when double-peaked spectra are observed, and that seems to affect wave height exceedance within the harbor. In this paper, the occurrence frequency of the double-peaked spectrum is estimated by using newly proposed method. Moreover, the estimation of the probability of wave height exceedance within the harbor is carried out with considering both the separated significant periods of wind wave and swell from the double-peaked spectrum. On a berth in the target harbor, it reduces 0.1% when the number of underestimation of significant wave periods is 2% in whole observed spectra.

Consideration of Design Wave for Port Construction according Recent Observation

The characteristics of swell are estimated by using the observed wave height data classified by wave period range in NOWPHAS (Nationwide Ocean Wave information network for Ports and HarbourS). Estimated characteristics demonstrate that the direction of swell is approximately derived by using the location of typhoon. As a result of directional spectrum analysis, the design condition for swell are expressed as JONSWAP spectrum with wave angle spreading parameter Smax = 50 ~ 75.

Estimation of Transmitted Waves by Overtopping Based on Field Observation and Model Experiment and Simple Approach in Numerical Simulation

Katsuya HIRAYAMA, Junzo HASEGAWA, Iwao HASEGAWA, Tetsuya HIRAISHI Transmitted waves by overtopping over a breakwater sometimes affect safe navigation and mooring of aship. In this paper, they are evaluated by wave data analysis in a field observation provided at both inside and outside of the breakwater where the wave overtopping is frequently observed. And their significant heights can be estimated by the approximate formula obtained in the model experiment conducted with a thin vertical breakwater in section. On the other hand, the results of the model experiment are reproduced by numerical simulation using the Boussinesq-type wave transformation model equipped the wave overtopping model proposed by Hirayama et al (2006). Therefore, their spreading on Sakata port is calculated by the Boussinesq model with an assumption the offshore breakwater is thin.

EXPERIMENTAL STUDY ON STABILIZATION OF ARTIFICAIAL BEACHIN CORAL REEF

For artificial beach constructed in coastal region facing to a coral reef, the stability of sediment is most important Meanwhile, the beach should be convenient for amenity activity and valuable to natural landscape. In order to protect the beach erosion in such artificial beaches, several countermeasures are proposed and carried out. The head land method is one of the most effective way for beach stability. This paper proposes the new effective arrangement of head lands to protect the artificial beach planed in coral reef employing the three dimensional experiments. In the experiment the level of flow which caused the beach erosion are determined in the two dimensional cannel tests.

Experimental Study on Sediment Movement in a Channel with Model Reef

An artificial beach has been constructed in coastal region facing to a coral reef. To prevent beach erosion, characteristics of sediment movement on the beach should be investigated in flume experiments. The watervelocity becomes very large with wave breaking zone on the reef. Therefore, the critical amplitudes of velocity on reef should be defined for the promotion of beach protection methods. The-experiment results demonstrate that the critical velocity is related to the shields number.